A variety of screw conveying apparatuses have heretofore been used or proposed for use in conveying various flowable materials through a chamber in which they may simultaneously undergo processing through heat exchange in which the material is heated to elevated temperatures. A continuing problem associated with such screw-type conveying apparatuses is the tendency of the material being conveyed or processed to accumulate or become encrusted on the surfaces of the worm or helical auger substantially reducing the conveying efficiency and further causing large variations in the degree of processing to which the materials are subjected.
In recognition of this problem, various screw-type conveying devices have heretofore been proposed which employ a plurality of intermeshing screws or worms which are arranged so that the helical surfaces of the adjacent screws come in contact with each other to impart a scraping action effecting dislodgement of encrustations of accumulated materials thereon. This has been achieved by varying the relative speed of rotation of adjacent screws which may rotate in the same direction or in counter directions as well as by effecting a relative reciprocation of one screw to the other imparting a traversing movement of their helical surfaces. Typical of such prior art constructions are those shown and described in U.S. Pat. Nos. 2,788,195; 3,255,814; 3,506,066; 3,549,000; 3,580,389 and 3,637,069.
In screw conveyor apparatuses of the types described in the aforementioned United States Letters Patent, the use of a plurality of intermeshing screws necessitates a housing of a complex cross sectional configuration to accommodate the several screws with the peripheral edges thereof in close fitting relationship to the inner surfaces of the housing to prevent excessive leakage of the material being conveyed under pressure between the screws and housing. This necessitates a relatively costly structure. In addition, the use of differential speed drive mechanisms to vary the speed of rotation of adjacent screws or to effect axial reciprocation of one screw relative to the other requires very complicated and costly mechanisms to assure proper operation further detracting from the economy of such apparatuses.
The present invention overcomes many of the problems and disadvantages associated with prior art type screw conveyor apparatuses incorporating self-cleaning characteristics by employing a single screw or helical flight enabling use of a conventional circular cylindrical conveying chamber and wherein the cleaning action can be effectively restricted to only those sections of the screw at which objectionable accumulations of material occurs by a mechanism which is relatively simple and inexpensive, of durable construction, of efficient operation, and which can be adapted to apparatuses operating under relatively high pressures and temperatures.